# Unlimited mass can have not gravity

1. Mar 11, 2009

### Jarritos

Me and a friend where talking and he was saying that something that has unlimited mass can have not gravity. This notion goes against pretty much everything I was taught in school. So my questions is this theoretically possible?

2. Mar 11, 2009

### itsme

Re: Gravity

nothing can earn the mass of infinity according to the law of relativity so it is not theoretically possible to prove this

3. Mar 11, 2009

### neu

Re: Gravity

(I know next to no cosmology, please fill me in on my mistakes) Well, the nearest real concept that I can think of to an infinite mass object is a black hole, i.e. finite mass at a singularity, which clearly has gravity. We're orbiting a big fat one(s) right now.

4. Mar 11, 2009

### Subductionzon

Re: Gravity

A black hole does not have infinite mass at the singularity, it sometimes is said to have an infinite force of gravity at the singularity. Those are two very different things. Also if you throw something into a black hole from a safe distance you will never see it actually go into the black hole. The light that it reflects will be red shifted from here to eternity and if you have a sensitive enough device it will always "see" the object falling into the black hole.

5. Mar 11, 2009

### Kurdt

Staff Emeritus
Re: Gravity

Black holes do not have infinite mass.

6. Mar 11, 2009

### neu

Re: Gravity

Notice the word finite before mass in my post. You both apear to think I said infinite, I did not.

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7. Mar 12, 2009

### pallidin

Re: Gravity

I would agree that "infinite mass' is theoretically impossible, thus any considerations about it might be considered essentially irrelevant.
But that's only a point-of-view, and I could be wrong.

8. Mar 12, 2009

### v2kkim

Re: Gravity

The BH at our galaxy center is known to have 4 million times mass of the sun, and some BHs have billion times of sun, so their mass is huge though not infinity.

9. Mar 12, 2009

### Archosaur

Re: Gravity

It is not possible to have infinite mass, but you can write a limit:

$${Lim}_{M\rightarrow\infty}{G}\frac{{M}\cdot{m}}{R^{2}}=\verb!a s#&@ ton of gravity!$$

10. Apr 5, 2009

### itsme

Re: Gravity

not only the black holes but actually nothing have infinite mass according to the laws of relativity of mass

11. Apr 5, 2009

### isabelle

Re: Gravity

I don't know any reason infinite mass is ruled out in theory, but thanks to modern cosmology we know that the total amount of mass-energy in the visible universe is finite.

In the standard model mass is a lorentz invariant scalar quantity, so there is no 'relativity of mass' i.e. mass is invariant under the actions of the lorentz group.

In physics units $\hbar = c = 1$ there is only one kind of dimensionful quantity, energy (which has the same units as mass) or the reciprocal of energy which is distance (which has the same units as time). In other words, since mass has units we can always choose the system of units so that the masses that appear in our equations are arbitrarily large numbers, and the laws of physics are unaffected by a chang of units.

When we solve the planetary orbit or the hydrogen atom, we use the reduced mass approximation with the sun/proton being infinitely heavy compared to th planet/electron.

Last edited: Apr 5, 2009